A. Field of the Invention
The present invention is directed generally to a method and apparatus to cut and remove well casing, and, more specifically, is directed to a method and apparatus to cut well casing and extract it from the well bore in a single downhole trip. B. Background
In oil and gas exploration and development operations it is often desirable to remove casing which has previously been set in the wellbore. Casing removal requires that the casing string first be severed and the free end then pulled to the surface, to remove the severed portion.
Conventional apparatuses and techniques for extraction of well casing typically involve the use of multiple trips to move cutting and extracting equipment downhole. Thus, in removal operations a casing cutter is first lowered into the wellbore to cut the casing at a desired depth after which time the cutter is returned to the surface. A spear is then lowered inside the well and engaged to the free end of the casing. Once the free end of the casing is engaged, an attempt is then made to recover the casing by pulling, or, in the case jars are used, by a combination of pulling and jarring. If these attempts to remove the casing are unsuccessful, the spear assembly is removed from the wellbore and the cutter reattached to the workstring to sever the casing at a point above or below the original cut. The pulling/jarring process is then repeated until the casing is recovered.
Such prior art apparatuses and techniques for retrieving well casing suffer from the disadvantage of the overall time and costs involved in completing a casing extraction. This time and expense is a result of the utilization of separate cutting and extraction tools which must be independently run downhole. Even when casing is retrieved without the need to complete a second cut of the casing, at least two trips are necessary for a complete cutting and retrieval operation. When a significant length of casing is extracted, considerable rig time must be used to move the tools downhole to the site of the cut. Time and expense are therefore increased when multiple cuts are necessary to retrieve the casing.
Additionally, systems for cutting and removing casing have been proposed wherein a grapple assembly or "spear" is adapted to be inserted in the top portion of the casing, with the degree of insertion of the spear into the casing limited by a stop ring. The spear in such systems is a mechanically actuated spear, which is actuated through use of interference. between the spear grapple and the casing, and through manipulation of the workstring. Such systems offer the disadvantages that there is a fixed distance between this stop and the cutting elements. Accordingly, when the grapple is placed inside the casing (and its depth is established by the placement of the stop), there is a fixed depth that which the cutter can be placed. Accordingly, if the first attempt to free the casing is not successful, this type of tool must be pulled out of the hole, and the distance between the grapple stop and cutting elements either lengthened or shortened to facilitate another cut of the casing at a different depth.
Accordingly, the present invention provides a new method and apparatus whereby casing may be cut and pulled with the string in tension, and whereby the grapples may be placed at virtually any desired location within the casing, allowing multiple attempts to cut and pull the casing on a single trip of the workstring into the wellbore.